Human vibration

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As human vibrations mechanical be vibration ( vibration , shock, shock) designated acting externally on humans, for example, when working on machines or in vehicles . Depending on the part of the body exposed to vibration, a distinction is made between whole-body vibrations (GKS, introduction point: buttocks, feet) and hand-arm vibrations (HAS, introduction point: hands). The amount of vibration exposure depends on the intensity (amplitude), frequency, type of vibration (harmonic, stochastic, shock-containing) and its direction of vibration (vertical, horizontal). Other stress factors are an unfavorable posture and high coupling forces. The duration of the vibration exposure is also of great importance.

Damage caused by work-related vibrations is considered an occupational disease . Requirements for occupational health and safety for Germany are regulated in relation to the effects of vibration in the Noise and Vibration Occupational Safety and Health Ordinance and the Health and Safety Mining Ordinance. Information on the implementation of the regulation (risk assessment as well as measures to reduce mechanical vibrations) can be found in the technical rules for the noise and vibration occupational safety regulations (TRLV Vibrationen).

In order to take into account the effect on the human body, the acting accelerations are evaluated with different frequency curves depending on the place and direction of the effect . The influence of the exposure time is taken into account by averaging over a working day of eight hours.

Whole body vibration

Vibration exposure on a forklift

Vehicle drivers and passengers of land, water and air vehicles are exposed to mechanical whole-body vibrations (frequency 1 to 80 Hz). In addition, vibrations from stationary machines such as punching , forging hammers or presses can affect people. The whole-body vibrations also include low-frequency vibrations (<1 Hz), to which, for example, ship personnel are exposed; they can cause motion sickness (kinetosis).

It is estimated that around 1.5 million employees in Germany are exposed to whole-body vibrations in the workplace, with drivers of military vehicles , earth-moving machines , construction site trucks, agricultural tractors and forklifts being the most exposed ( a wz = 1 to 2.5 m / s²). Particularly high vibration accelerations (a wz approx. 1.5 to 3 m / s²) occur with forklifts in outdoor areas on uneven surfaces (pavement) or when driving over rails. Earth-moving machines, for example bulldozers (a wz approx. 1 to 1.5 m / s² on hard surfaces) or dump trucks with long operating times are also affected.

According to the Noise and Vibration Occupational Safety and Health Ordinance and the Health and Safety Mining Ordinance, two values ​​must be used in Germany to assess the health risk. The trigger value of the evaluated vibration acceleration is based on an 8-hour working day at 0.5 m / s². The exposure limit depends on the direction of the vibration exposure. In the longitudinal direction (z) of the spine it is 0.8 m / s² and in the transverse directions (x or y) 1.15 m / s². The exposure limit value of the EU directive on vibrations has been set at 1.15 m / s² and is thus partly above the limit applicable in Germany.

The Institute for Occupational Safety and Health of the German Statutory Accident Insurance (IFA) has developed a debit display to illustrate vibration loads when operating vehicles . This device measures whole-body vibrations in three axes using a measuring disc on the driver's seat and uses a traffic light diagram on a screen to inform the driver of the current vibration exposure. If this is above the exposure limit value, the display is red; if only the trigger value is exceeded, it appears yellow, with green underneath.

The device has a daylight-compatible display , can be easily and safely attached in the driver's cab and has a simple one-button operation for all functions (switching on, measuring start, measuring stop and switching off). Employees can feel, see and evaluate their personal vibration exposure. It is also immediately apparent how changed driving styles or seat settings affect the vibration exposure.

Vibration reduction through adapted suspension seats - driver's seats

Air-cushioned suspension seat with fully automatic adjustment for the driver of a forklift truck

The risk to health can be reduced considerably through design changes to vehicles and systems, but above all through the use of adapted driver's seats. In particular, air-cushioned suspension seats (passive damping) achieve reductions of up to 60%, depending on the frequency and the driver's weight. More recent developments are moving in the direction of active damping on suspension seats in order to minimize hazards. Mechanical suspensions of suspension seats are only suitable to a limited extent if there are assumed health hazards above the release values ​​and do not achieve the reductions in air-suspension seats.

The reduction in vibration acceleration on a passively damping suspension seat is heavily dependent on the stimulation that the seat receives from a vehicle or machine. If the vibration excitations are in high frequency ranges (> 20 Hz), a high reduction is to be expected; if they are lower (<5 Hz), the vibration damping depends on the distance to the natural frequency of the suspension seat, which should be at least three times the natural frequency of the seat. Typical natural frequencies for passive air suspension seats are between 1 and 2 Hz. The selection and adaptation for machines and vehicles must therefore be preceded by the detection of the typical vibration excitations when the device is used at the place where the seat is installed. For example, the vibration excitations on an asphalt road differ from those on the terrain or the road surface when raw materials are extracted in open-cast or underground mining .

Another important point is the dependence of the vibration reduction on the driver's weight. Most seats have a weight adjustment option. However, optimal results in practice are only achieved on air-cushioned suspension seats with fully automatic electronic weight adjustment. This determines the setting automatically when the vehicle is started or the seat is activated. Only in this way can reductions in vibration acceleration in the order of magnitude mentioned over longer periods of time be ensured in practical operation.

Depending on the load, suspension seats have a reducing effect that decreases over their service life , often due to increased internal friction, so that depending on use, it may be necessary to replace the seats on machines and devices. This applies in particular to forklift trucks and caterpillar vehicles such as bulldozers, which, depending on the load, can already lead to limitations in the reduction effect after 2000 to 3000 operating hours. In the case of continuous use of forklifts or caterpillars, there is also the fact that the attachment points can deflect and this leads to relative movements which then even increase the vibration exposure and cause additional impulses.

Hand-arm vibrations

Vibration exposure when working with the angle grinder

Due to the increased use of hand-held or hand-held tools ( e.g. rotary hammer , chainsaw , grinding machine, chisel hammer), an ever increasing number of workers are exposed to hand-arm vibrations (HAS). It is estimated that around 18% of employees in Germany are exposed to hand-arm vibrations (frequency: 8 to 1,000 Hz).

According to the Noise and Vibration Occupational Safety and Health Ordinance in Germany, the trigger value for hand-arm vibrations is 2.5 m / s² and the exposure limit value is 5 m / s². Both figures relate to an 8-hour working day.

In order to determine the daily vibration load of a work machine, you can use a characteristic value calculator, which is made available as an Excel table by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA). For this, the vibration effects of the machine used and the associated exposure times must be known. A vibration exposure calculator with a checklist and other information helps set up a vibration reduction program.

consequences

Both hand-arm and whole-body vibration loads not only lead to acute physiological stresses (increased muscle reaction, reduced performance) and impairment of well-being in humans, but can also cause chronic complaints, i.e. damage to health, after long-term exposure. Long-term exposure to vertical vibrations while sitting can lead to degenerative changes in the area of ​​the spine in humans . In Germany, the disease caused by whole-body vibrations has been included in the BeKV occupational disease ordinance as occupational disease BK 2110 " Disc- related disease of the lumbar spine caused by long-term, predominantly vertical effects of whole-body vibrations while sitting ...". Vibration loads in the hand-arm system can cause degenerative changes in the bones and joints (occupational disease BK 2103) at low frequencies (below 50 Hz). Vibrations with frequencies above 20 Hz can lead to circulatory disorders and nerve dysfunction (occupational disease BK 2104: vibration-related vasospastic syndrome ; also known as white finger disease ). In order to be able to record and estimate the vibration risks, technical test procedures and occupational health assessment procedures have been established, which are included in various national ( e.g. VDI guideline 2057-1) and international standards and guidelines ( e.g. ISO 5349-1, EN 28662, ISO 2631 -1) were written down.

literature

Web links

Individual evidence

  1. ↑ Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA): GKV load display - A simple device for displaying whole-body vibrations. Retrieved August 13, 2018 .
  2. ↑ German Social Accident Insurance eV (DGUV): Make awareness of vibration exposure. In: DGUV Forum 10/2017. Retrieved August 13, 2018 .
  3. ↑ Institute for Occupational Safety and Health of the German Statutory Accident Insurance (IFA): Risk assessment for hand-arm vibrations - Simple determination of hand-arm vibration loads. Retrieved August 13, 2018 .